In order to stably operate a railroad vehicle, it is necessary to grasp information on accurate positions of all of railroad vehicles traveling on the entire tracks. In general, among methods for detecting positions of railroad vehicles traveling on tracks, a track circuit method is well known.
However, the conventional method renders several disadvantageous in that only the positions of vehicles ranging from several hundred meters to several kilometers can be discriminated due to characteristics of a track circuit, and the effectiveness is poor because of a risk of occurrence of electronic waves or malfunctioning of a track circuit due to the use of an electrical contact method for position detection, installation and maintenance of the track circuit are not easily achieved, and installation and maintenance costs are considerably high.